Electron tube with cathode support ring having outwardly extending support legs,channel-shaped in cross section and a u-shaped yoke supporting the control grid



W. R. STUART May 20, 1969 ELECTRON TUBE WITH CATHODE SUPPORT RING HAVINGOUTWARDLY EXTENDING SUPPORT LEGS, CI IANNNEL-SHAPED IN CROSS SECTION ANDA U; SHAPED YOKE SUPPORTING THE CONTROL GRID Original Filed Dec. 27,1962 I Sheet 9 V 5+! 8 N A x 2 777 1L z 7x a \VQKV/IW x! M "xvi: P I) 7,I 4 Rx U 54 3 2 I \0\ w u a H 4 5 {ll 4 H llllll ilk y a I M I r I i 5w Hui r- IA INVENTOR. WILLIAM R. STUART wise/1a ATTORNEY May 20, 1969 w.R. STUART 3,445,712

ELECTRON TUBE WITH CATHODE SUPPORT RING HAVING OUTWARDLY EXTENDINGSUPPORT LEGS, CHA EL-SHAPED IN CROSS SECTION AND A U-S PED YOKESUPPORTING THE CONTROL GRID Original Filed Dec. 27, 1962 sheet 3 or:

INVENTOR. WILLIAM R. STUART Maw 81% ATTORNEY May 20, 1969 w. R. STUART3,445,712

ELECTRON TUBE WITH CATHODE SUPPORT RING HAVING OUTWARDLY EXTENDINGSUPPORT LEGS, CHANNNEL-SHAPED IN CROSS SECTION AND A U-SHAPED YOKE vSUPPORTING THE CONTROL: GRID Original Filed Dec. 27. 1962 Sheet 3 of ss4 9/ Y 0 n 65 as 40 l s I A860 INVENTOR. WILLIAM R. STUART v Maw-8%ATTORNEY Patented May 20, 1969 3,445,712 ELECTRON TUBE WITH CATHODESUPPORT RING HAVING OUTWARDLY EXTENDING SUPPORT LEGS, CHANNEL-SHAPED INCROSS SECTION AND A U-SHAPED YOKE SUPPORTING THE CONTROL GRID William R.Stuart, San Carlos, Calif., assignor, by mesne assignments, to VarianAssociates, a corporation of California Original application Dec. 27,1962, Ser. No. 247,718, now Patent No. 3,308,521. Divided and thisapplication June 22, 1966, Ser. No. 574,487

Int. Cl. H01 1/88, 19/42 US. Cl. 313250 6 Claims ABSTRACT OF THEDISCLOSURE An electron tube with cathode and control grid supports of aparticular shape and design. The cathode support consists of a ring withoutwardly extending support legs, channel-shaped in cross section sothat they can straddle and thereby make contact with their respectiveterminal pins. Also, the control grid is supported on the coaxialterminal pin by a U-shaped yoke.

This is a division of application Ser. No. 247,718, filed Dec. 27, 1962,now Patent No. 3,308,521.

This invention relates to electron tubes and more particularly to animproved tetrode of the type known in industry as the 4Xl50 series anddescribed in the patent to Drieschman et al., No. 2,472,942, issued June14, 1949.

The 4X150 type of tube construction has been widely used over the years.However, recent requirements have made it necessary for the tubes to beable to meet new specifications calling for ability to withstand extremeshock and vibration and also requiring improved accuracy in electrodealignment.

Accordingly, the object of this invention is to provide a new 4X150 typetube having improved ability to withstand shock and vibration, improvedconstruction for obtaining precise electrode alignment, and a method ofmaking the tube which provides the specified improvements and providesthem in an economical manner.

The problem has been to obtain the desired improvements withoutdeparting from the terminal arrangement and general internal andexternal configuration of the conventional 4Xl50 type tubes. The reasonof course is that considerable time and money has been invested in thedesign and construction of equipment which uses the 4X150 tube type. Theimproved tube according to this invention is therefore designed to beusable in existing equipment.

The specific construction which provides the desired improvements willbe hereinafter described in detail, and where possible comparison willbe drawn to prior 4X150 type construction.

These and other objects and features of advantage will become apparentfrom a reading of the following detailed description wherein referenceis made to the accompanying drawings in which:

FIGURE 1 is a cross sectional view on the centerline of an improved tubeaccording to the invention;

FIGURE 2 is a bottom view of the tube of FIGURE 1;

FIGURE 3 is a view on line 33 of FIGURE 1 showing a stage ofconstruction called the header assembly;

FIGURE 4 is a cross sectional view of the header assembly in a jig forassembling it;

FIGURE 5 is a top 'view of FIGURE 4 with the ceramic header disk and allparts above it removed;

FIGURE 6 is a side elevation of the header assembly from another anglewith parts cut away and showing the cathode and cathode jig in position;and

FIGURE 7 is a view similar to FIGURE 6 but showing the control grid andcontrol grid jig in position.

Referring in more detail to the drawings, an attempt will be made todescribe first the construction which is either shown in the Drieschmanet a1. Patent No. 2,472,942 or utilized in improved versions thereofprior to this invention. The tube of FIGURE 1 comprises a heater coil 1,a cathode 2, a control grid 3, a screen grid 4 and an anode 5.

The envelope for the tube is formed in part by the inverted cup-shapedmetal anode 5. The remainder of the envelope is formed by the metal ring7, brazed to the bottom of the anode and to the top of a ceramiccylinder 8 which is metalized in conventional manner for this purpose; ametal sealing ring 9 and a metal shell 10 which are sealed together by afinal braze or weld 11, with ring 9 being brazed to the bottom ofceramic cylinder 8 which is metalized for this purpose; and a ceramicheader disk 12 which has an annular metalized area brazed to shell 10.

As regards terminals for the electrodes, the outer portion of the anodeof course serves as its own terminal. The ring 9 and shell 10 can serveas the terminal for the screen grid 4. The remaining terminals areformed by pins sealed in the header disk 12. Eight small diameter pins14-21 are arranged in a circular array around a large diameter centerpin 22. Although eight small pins are employed only six of them arerequired as terminals. In the construction shown, pins 14, 16, 18 and 20serve as cathode terminals and pins 17 and 21 serve as heater terminals.In the preferred design, pin 19 serves as the screen grid terminal bymetalizing a conductive strip 23 on the bottom of header 12 from the pinto the metal shell 10. The center pin 22 is the control grid terminal.The center pin is sealed in the header by metalizing the wall of theaperture in the header and brazing the pin thereto. In the case of thesmall pins the aperture in the header are not metalized but instead anannular area is metalized on the bottom of the header around each pin. Acopper washer 24 is brazed to the metalizing and the pin, and a Kovarwasher 25 is brazed to the copper washer and to the pin.

The anode structure is completed by brazing on conventional metalcooling fins 27 and a two-piece metal cover 28 over the pinched-offexhaust tubulation 29. The anode structure is preferably impact formedso that the tubulation 29 can be made as an integral part thereof.

The cathode 2 is an inverted cup-shaped metal can having an electronemissive coating on its outer surface. The heater 1 is brazed or spotwelded at its opposite ends to two metal posts 31 and 32. A ceramic disk33 is apertured to receive posts 31 and 32 and serves as a heat barrierand shield. The disk is attached to the posts by two small wires 34which pass through apertures in the disk and are spot welded at each endto the posts. A conventional getter strip 35 is spot welded to post 32.The grids 3 and 4 are conventional cage-type wire structures, eachhaving an inverted cup-shaped configuration. It will be noted that thescreen and control grids and the cathode all have metal end portions 36,37 and 38, respecti'vely.

Control grid 3 is supported by means of a metal ring 40 attached to thebottom thereof and having two downwardly extending projections 41 on itsdiametrically opposite sides (only one such projection being visible inFIGURE 1). A supporting yoke structure is formed by two U-shaped rods 42brazed at their ends to the projections 41 and at their center in a slotin the top of the center pin 22. Although the construction thus fardescribed is not exactly the same in all respects as prior structures,it does not involve features which are claimed per se as new herein.

The improved features according to the invention will now be described.Starting with the cathode support, it will be noted that the cathodesupport ring 44 has four channel-shaped legs 45. It is important thatthe channel construction extends along the sides of the pins 14, 16, 18and 20. The reasons why this construction is important are that it makesit possible to braze the legs 45 to the pins and makes a much more rigidstructure. In the past, legs similar to legs 45 have been spot welded tothe pins. This not only involves four spot welds contrasted to a singlebraze step but more importantly often results in distortion of the legs.Although in the past legs similar to legs 45 have been ribbed along thefree portion thereof for rigidity, they Were flat where attached to thepins. It has been found that extending the channel shape along the sidesof the pins solves the rigidity problem whereas the prior constructiondoes not. In addition, the new channel construction simplifies assemblyby providing a socket in the end of each leg which receives the end of apin so that the problem of holding the legs oriented in place on thepins during attachment is avoided. Also the new construction provides acavity in which to place the brazing material which joins the legs andpins.

At this point it is desirable to recall that the general purpose of theinvention is to provide an improved construction which is physicallymore rugged, has more accurate electrode alignment and yet is simple tomanufacture. Many of the novel features of the invention are so designedas to combine all three of the described objectives. Thus, the shape ofthe cathode support legs accomplishes improved rigidity, improvedaccuracy in making the cathode prescisely coaxial with the tube, andimproved assembly technique.

Continuing with description of the cathode supporting means, a very thinmetal heat dam 46 is attached to the lower end of the cathode can. Thelower end of the heat dam is spot welded to the outer surface of thesupport ring 44. In the past the construction and assembly technique wassuch that the heat darn was attached to the inside of the support ring.As a result of this change the weld is made through the very thin metalheat dam and therefore can be a very light weld which does not distortthe members, thus insuring accurate positioning of the cathode.

Although the improvements already described result in substantialimprovement in the alignment, rigidity, and assembly technique for thecathode, the rigidity aspect is even further improved by a constructionwhich forms the cathode and heater into a composite assembly. The heaterposts 31 and 32 are brazed at their lower ends in legs 47 and 48. As inthe case of the cathode support legs, and for the same reasons, theheater legs are channelshaped including the portion which extends overand is brazed to the terminal pins 17 and 21, respectively. Oneimportant aspect of the cathode-heater combination is the use of aceramic rigidifying disk 50 which is metalized on its outer peripheryand brazed to the cathode support ring 44. The disk 50 is apertured toreceive heater posts 31 and 32, and the walls of the apertures aremetalized and brazed to the posts' Thus it will be appreciated that notonly are the cathode and heater supported individually in rigid mannerby channel-shaped legs brazed in place but these two structures arereinforced by the interconnection through ceramic disk 50. As a resultthe heater and cathode are firmly locked against movement relative toeach other or movement relative to the header disk 12.

The lower end of the screen grid 4 is attached to a metal cone 52mounted on a metal support ring 53. The cone is attached to ring 53 byscrews 54 (preferably three) which abut the cone and are received inthreaded apertures in the ring. Ring 53 has a three-part shapecomprising a cylindrical side portion 55 brazed to shell 10, a flatcone-supporting portion 56, and a downturned centering flange portion 57at its inner periphery. The importance of the centering function of thering 53 will become apparent when the assembly technique for the tube ishereinafter described. However, it will be noted at this point that theapertures for screws 54 are so positioned that when the screws areinserted in members 52 and 53, member 52 is centered with respect toflange 57.

Another feature of importance is the centering pin 60. Pin 60 is made ofceramic and its periphery is metalized where it pases through the screenand control grid ends 36 and 37 and is brazed to these ends. Theapertures in in the cathode and grids are centered in these electrodesand have a snug fit with the pin 60. In addition the pin has a largedisk portion 61 between the cathode and control grid to reduce thecapacitance between these electrodes. It will be understood that pin 60contributes materially to precise alignment of the cathode and grids andto the rigid interconnection of these electrodes.

The improved construction thus far described makes it possible toassemble the electrodes in a simple and accurate manner. In the past itwas necessary to assemble the tube in a much more complicated andtedious manner. For example, two separate spot welds were required toattach the heater legs 47, 48 to the heater pins, and four separate spotwelds were required for the cathode legs 45. Then as a result of thedistortion caused by the welds, it was necessary for highly skilledlabor to bend the legs with tweezers to align the heater and cathodevisually with the tube axis. The control grid was mounted on yokes 42and projections 41 were bent where necessary to make the control gridapproach concentricity with the cathode. Since the results of this handalignment were very often imperfect, it became necessary to hand pick ascreen grid which, when mounted on ring 53, would have distortionsmatching those of the cathode and control grid, or it was necessary torebend the cathode and control grid to match the mounted screen grid.

The improved construction makes it possible to assemble in a jig andconnect in a single braze all the following parts, called the headerassembly 62 as indicated in FIG- URES 3 and 4: shell 10; pins 14-22;washers 24 and 25; heater posts 31 and 32; control grid yokes 42;cathode support ring 44 with legs 45 fitted over their respectiveterminal pins; legs 47 and 48 fitted over their respective pins; ceramicdisks 33 and 50; and the centering and screen support ring 53. All ofthe previously described brazes involving these various parts are madein this single brazing operation except that it has been foundconvenient to form the heater-post assembly in a preceding operation.More specifically posts 31 and 32, ceramic disk 33, wires 34, ceramicdisk 50, and legs 47 and 48 are preferably prejoined with highertemperature bonds. The centering flange 57 provides a relatively largeinner surface which can be formed to close tolerance, retain such size,and provide a relatively large reference surface for centering the topsof the cathode and control grid when they are attached to the headerassembly, as will be hereinafter described.

FIGURES 4 and 5 show the jig for performing the assembly techniquedescribed in the preceding paragraph. As shown in FIGURE 4 the headerassembly parts are mounted upside down in the jig. More specifically,the jig comprises a bottom portion having a base 66 with a cylindricalprojection 67, and an inner sleeve 68 held by pins 69. The upper portionof the jig comprises a weight and centering ring 71, a pin holding ring72 and a Weight 73. FIGURE 5 is a top view of FIGURE 4 with the headerdisk 12 and everything above it removed.

The jig centers, rotationally orients, and vertically positions theparts as follows. A bore 74 in base 66 centers the heater post 31. Abore 75 in sleeve 68 centers the cathode support ring 44. The rim 76 onprojection 67 centers the centering flange 57. The upper edge ofprojection 67 vertically positions the legs 45 and 47, 48. The fact thatlegs 45 are rigid means that when they are positioned on projection 67,the plane of the cathode support ring is exactly normal to the tubeaxis. A shoulder 77 on projection 67 vertically positions the screensupport ring 53. Upwardly extending projections 78, 79, 80 and 81vertically positionthe ceramic disk 12, and rotationally position thelegs 45 and 47, 48. The U-shaped rods 42 are rotationally and verticallypositioned by bores '82 in the upper end of sleeve 68. The parts areloaded into the jig in the following order: screen grid ring 53-,cathode support ring 44; heater assembly including legs 47 and 48;U-shaped rods 42; ceramic disk 12; pins 14-22; washers 24 and 25, andshell 10. Brazing material, preferably in paste form, is placed wherenecessary during assembly of the parts in the jig, and the loaded jig ispassed through a brazing furnace to provide the completed headerassembly 62. It should now be clear that when the header assembly isbrazed together in an accurate jig, the cathode support ring 44 isexactly centered and aligned with the centering flange 57.

Having thus fabricated the header assembly to accomplish the basiccentering with assurance, the cathode structure may be lowered intoplace with the heat dam 46 centering itself around the cathode supportring 44 to accomplish perfect centering of the bottom of the cathodestructure. The centering flange 57 is employed to accomplish perfectcentering of the top of the cathode by means of a jig 84 as shown inFIGURE 6. The jig comprises a cylindrical wall portion 85 having fourequally spaced legs 86 projecting therefrom, only two such legs beingshown in the drawing. Each leg has an accurately formed centering lip87, which engages the centering flange 57, and an abutment surface 88which rests on the flat portion 56 of ring 53. Mounted in thecylindrical portion 85 is a block 89 which engages the top of thecathode and insures that the cathode is pushed dow to the properelevation. Block 89 is preferably magnetic material to facilitateloading the cathode in the jig. A centering pin 90 is mounted in the jigin centered relation to centering lips '87 and engages the walls of theaperture in the top of the cathode can 2, the same aperture which laterreceives the ceramic pin 60. After the cathode, jig and header assemblyare positioned as shown in FIGURE 6, the heat dam 46 is spot welded tothe cathode support ring 44. The legs 86 are of course widely enoughspaced to permit insertion of the welding tool. The jig is then removedwith assurance that the cathode is perfectly centered and aligned topand bottom.

After the cathode is mounted, the control grid is positioned by a jig84' (FIGURE 7) similar to jig 84. The main difference in the jigs isthat the control grid jig has an aperture 91 in place of pin 90 in thecathode jig. The reason is that when the control grid is mounted theceramic pin 60 is prebrazed therein, and the pin 60 is simply receivedin the aperture 91 in the control grid jig. The remaining portions ofthe jig 84 are given primed reference numbers to designate parts similarto the parts designated with unprirned numbers in jig 84. In jig 84'there are prefera-bly only two legs 86', each being somewhat wider thanlegs 86. Legs 86 provide two openings for placing brazing material atthe joint between yoke rods 42 and the control grid projection 41. Itwill be noted that the aperture 91 is oversized with respect to pin 60and that the bore in the upper end of the cylindrical wall 85' isoversized with respect to the end 37 on the control grid. Thus, the topof the control grid is centered by reception of pin 60 in the aperturein the top of the cathode can, and bottom is centered by engagementbetween the jig wall 85 and the control grid ring 40. Projections 41 onthe control grid ring are then brazed to yokes 42 while the jig is inplace and then jig 84' is removed. The remaining parts of the tube arethen assembled in conventional manner except that pin 60 automaticallycenters the top of the screen grid 4.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is as follows:

1. An electron tube comprising a vacuum-tight envelope, a ceramic headerdisk forming one end of said envelope, a plurality of terminal pinssealed in said header disk and projecting therethrough on the inside andoutside of the tube, a cathode support ring in said tube and having aplurality of outwardly extending support legs, said legs beingchannel-shaped in cross section and each of said legs being brazed tothe inner end of a separate one of said pins, said legs being fittedover their respective pins with the side portions of each leg channelstraddling its respective pin, a ceramic disk metalized on its outerperiphery and brazed to the inner periphery of said support ring, a heatdam welded to the outer periphery of said support ring and extendingthereabove, a cathode can mounted on the upper end of said heat dam, aheater within said cathode can, support posts for said heater brazed inapertures in said ceramic disk, channel shaped legs on said posts brazedto the inner end of others of said pins, and an anode around saidcathode can.

2. An electron tube as claimed in claim 1 further comprising acylindrical control grid surrounding said cathode can, a cylindricalscreen grid surrounding said control grid, each of said grids having anend portion above said cathode can, one of said terminal pins beingcoaxial with said header disk and a U-shaped yoke supporting saidcontrol grid on said coaxial terminal pin, a centering and screen gridsupport ring having a cylindrical side portion surrounding the rim ofsaid header disk and having a downturned centering flange at its innerperiphery, said screen grid being mounted on said screen grid supportring, and a centering pin through and engaging the end portions of saidcathode can and said grids, said centering pin being coaxial with saidcentering flange.

3. An electron tube comprising a vacuum-tight envelope, a ceramic headerdisk forming one end of said envelope, a plurality of terminal pinssealed in said header disk and projecting therethrough on the inside andoutside of the tube, a cathode support ring in said tube and having aplurality of outwardly extending support legs, said legs beingchannel-shaped in cross section and each of said legs being brazed tothe inner end of a separate one of said pins, said legs being fittedover their respective pins with the side portions of each leg channelstraddling its respective pin, a ceramic disk metalized on its outerperiphery and brazed to the inner periphery of said support ring, a heatdam attached to said support ring and extending thereabove, a cathodecan mounted on the upper end of said heat dam, and an anode around saidcathode.

4. An electron tube comprising a vacuum-tight envelope, a ceramic headerdisk forming one end of said envelope, a plurality of terminal pinssealed in said header disk and projecting therethrough 0n the inside andoutside of the tube, a cathode support ring in said tube and having aplurality of outwardly extending support legs, said legs beingchannel-shaped in cross section and each of said legs being brazed tothe inner end of a separate one of said pins, said legs being fittedover their respective pins with the side portions of each leg channelstraddling its respective pin, a heat darn Welded to the outer peripheryof said cathode support ring and extending thereabove, a cathode canmounted on the upper end of said heat darn, a heater within said cathodecan, and an anode around said cathode can.

5. An electron tube as claimed in claim 4 further comprising acylindrical control grid surrounding said cathode can, a cylindricalscreen grid surrounding said control grid, each of said grids having anend portion above said cathode can, one of said terminal pins beingcoaxial with said header disk and a U-shaped yoke supporting saidcontrol grid on said coaxial terminal pin, a centering and screen gridsupport ring having a cylindrical side portion surrounding the rim ofsaid header disk and having a doWnturned centering fiange at its innerperiphery, said screen grid being mounted on said screen grid supportring, and a centering pin through and engaging the end portions of saidcathode can and said grids, said centering pin being coaxial with saidcentering flange.

6. An electron tube comprising a vacuum-tight envelope, a ceramic headerdisk forming one end of said envelope, a plurality of terminal pinssealed in said header disk and projecting therethrough on the inside andoutside of the tube, a cathode support ring in said tube and having aplurality of outwardly extending support legs attached to certain ofsaid pins, a cathode can mounted on said support ring, a cylindricalcontrol grid surrounding said cathode can, a cylindrical screen gridsurrounding said control grid, an anode surrounding said screen grid, acentering and screen grid support ring having a cylindrical side portionsurrounding said header disk and having a downturned centering flange atits inner periphery, said screen grid being mounted on said screen gridsupport ring, and a centering pin through and engaging the tops of saidcathode can and said grids, said centering pin and said cathode supportring being coaxial with said centering flange.

References Cited UNITED STATES PATENTS JOHN W. HUCKERT, PrimaryExaminer.

BARRY ESTRIN, Assistant Examiner.

US. Cl. X.R.

